It is not so much a matter of age, we al have frowns even our youngest offspring. We collected loads of frowns - actually landscapes on the forehead - and came to the conclusion that there are different frowns categories.
The most likely frown is the one with two lines straight up: "the bridge,". In addition, you could also discover 'highways', 'ally's', and 'crossroads'. Or a hairpin turn.
with Niels Stomps